Explosive type expansible plug



a 1970 J. J. BEsHARA EXPLOSIVE TYPE EXPANSIBLE PLUG Filed Jan. 17, 1967 United States Patent 3,491,798 EXPLOSIVE TYPE EXPANSIBLE PLUG John J. Beshara, Port Arthur, Tex., assignor to Texaco Inc., New York, N.Y., a corporation of Delaware Filed Jan. 17, 1967, Ser. No. 609,917 Int. Cl. F16] 55/12; F28f 11/00 US. Cl. 138-89 2 Claims ABSTRACT OF THE DISCLOSURE This invention concerns a method and apparatus relating to an expansible plug. More particularly, the invention concerns a plug structure and a method for employing same that is especially adapted for use with heat exchanger tubes or similar structures.

Heat exchangers of the type to which this invention is especially applicable, are constructed with a large number of relatively small diameter tubes situated in a group that is commonly called a bundle. Heat is exchanged between fluids flowing inside and around the outside of the tube bundle. And, the fluids are maintained physically separated by using so called tube sheets, one at each end of the tube bundle. Consequently, it is common practice to repair a leaky tube by plugging it off at each end, and

thus eflectively removing it from service while still leaving it physically in place. However, in order to get access to the open ends of such a tube there is a lot of time consuming work involved in removing the covering structure over the tube sheets. Furthermore, while some attempts have been made to plug the far end of a tube so that only the covering at one tube sheet need be removed, this has been found to be quite diflicult and time consuming as well as resulting in a plug that tends to leak under pressure.

However, in regard to latter (far end) type of plugging, it will be found that by employing a plug according to this invention the time and effort may be at least halved. This is so because a simple yet rapidly applied and completely effective plug may be inserted from the far end of a tube, and then quickly and easily expanded in place. Also, it will be appreciated that under these circumstances the necessity of either pulling the tube bundle or of removing outer and inner covers at one end, may be entirely avoided. This eliminates the need for a substantial amount of man-hours in maintaining this type of equipment in operating condition. Furthermore only a simple type of tool is needed to insert a plug and it may be operated by one man.

Consequently, it is an object of this invention to provide an explosive type of expansible plug that may be employed to create a pressure resistant seal to close oif one end of a heat exchanger tube, within the tube sheet to which it is attached.

Another object of the invention is to provide an explosive type of soft metal plug that may be remotely detonated and that includes means for centering same within a heat exchanger tube.

Briefly, the invention concerns an expansible plug for use in heat exchanger tubes or the like, which comprises a cylindrical body having an outside diameter over the entire lengh thereof that is slightly less than the inside diameter of one of said tubes. The plug also comprises an explosive charge withine said body, said body being constructed of ductile material having sutficient wall thickness to avoid rupture when said charge is detonated. The plug also comprises means for detonating said charge when the plug is in place within a tube.

Again briefly, the invention concerns a method of plugging a leaky tube in a heat exchanger or the like, wherein said tube is attached at at least one end thereof to a tube sheet. The method comprises the steps of taking an explosive type of plug having a charge therein, and inserting and coaxially centering said plug within said tube. The method also comprises the steps of locating said plug so that said charge is within said tube sheet, and detonating said charge to plug the end of said tube within said tube sheet.

The foregoing and other objects and benefits of the invention will be described in greater detail below and will be set forth in connection with the best mode contemplated by the inventor of carrying out the invention, and in connection with which there are illustrations provided in the drawings, wherein:

FIG. 1 is an elevation largely broken away in longitudinal cross-section, illustrating a typical heat exchanger having both stationary and floating tube sheets with a bundle of tubes between and to which structure the apparatus and method of subject invention is applicable;

FIG. 2 is an enlarged elevation illustrating schematically a plug according to the invention, having a flexibleshaft type tool for inserting the plug within a tube, shown partly broken away in cross-section;

FIG. 3 and FIG. 4 are cross-sectional views taken along the lines 33 and 44 of FIG. 2 looking in the direction of the arrows;

FIG. 5 is an enlarged scematic longitudinal crosssectional view illustrating a plug according to the invention, in place within a tube and inside the tube sheet at one end of the tube; and

FIG. 6 is a similar view as FIG. 5 but showing the plug after it has been expanded by detonating its charge.

FIG. 1 illustrates a typical heat exchanger unit 15 to which an explosive plug according to this invention is particularly applicable. It will be observed that a heat exchanger of this type provides for exchange of heat between two fluids, one of which flows through the interior of a cylindrical bundle of tubes 11, while another fluid flows over the exterior of the tubes 11 within a shell 12. The shell 12 has nozzles 13 and 14 for connecting the one fluid to the inside of the shell.

The fluid flowing through the interior of the tubes 11 is directed to pass back and forth through a series of different groups of the tubes by reason of providing the necessary pass partitions at the ends of the tubes. Thus, at one end of the heat exchanger 15 there is a so-called stationary head 17 with an inlet 18 attached thereto. This head has a number of pass partitions such as a partition 19, as shown, that will direct the fluid through a path within the uppermost group of tubes. That uppermost group of tubes are connected to the interior of the stationary head -17 above the partition 19, since these tubes are fastened to a stationary tube sheet 22 that forms one wall of the interior of the stationary head 17.

At the other end of these tubes they are attached to a floating tube sheet 23 as also are all of the tubes 11 in the bundle.

The flow reverses direction within the interior of a floating head 24 that is associated with tube sheets 23 and has a pass partition 27 which divides the interior of floating head 24 in two. Consequently, the fluid flowing within the tubes 11 above the stationary head partition 19 will return after reaching the upper portion of the interior of floating head 24, through the group of tubes 11 that are located below the partition 19 but above the partition 27.

Then a similar flow path is provided to allow the fluid flowing into the middle portion of stationary head -17, i.e. beneath the partition 19, to flow back through the group of tubes 11 that connect this space with the lower portion of the interior of floating head 24 (beneath partition 27). Thereafter the fluid will flow back again through the group of tubes that are located beneath another partition (not shown) like the partition 19. This additional partition is located symmetrically in the lower portion of the interior space within stationary head 17. From there the fluid flows out through an outlet 28.

The other fluid will flow in contact with the outside of the tubes 11 of the bundle. The flow path for this other fluid is from the nozzle 13 into the interior space of the shell 12. Then because of a series of bafi'les 31 this fluid will flow over a tortuous path along the length of the interior of shell 12. It will then flow out through nozzle 14 near the other end of the shell from the inlet nozzle 13.

It will be appreciated that there are a large number of the tubes 11 in an entire bundle within a heat exchange unit. For this reason it is common practice to overcome a leak in any given tube by merely blocking off the interior of such tube by plugging the ends at the tube sheets. In this manner, a given tube which has developed a leak is isolated and effectively removed from the flow path for the fluid passing through the interior of the tubes. The remaining tubes of the bundle continue to act in the normal manner to provide heat exchange as desired.

While this expedient of plugging a leaking tube is relatively effective in extending the useful life of a given heat exchanger, the time and effort involved in carrying out the plugging of both ends of a given tube is quite considerable. This will be fully appreciated when it is noted that not only must the heat exchange unit be shut down, but one end or the other must be opened with covers removed to have access to the open ends of the tubes. Furthermore, unless both ends of the tubes are uncovered for access thereto; it has been found in past experience most difficult, if not entirely impractical, to attempt to plug securely in a leak-proof manner the far end of any given tube. Consequently, by employing a plug and carrying out the method in accordance with this invention, it will be found that the time and effort is reduced to one-half, in plugging off a given tube of a tube bundle in a heat exchange unit.

Referring now to FIGURES 2 through 6, the structure involved in a typical explosive plug according to the invention will be described. While the interior explosiverelated elements of a plug and the design thereof form no part per se of the invention, a plug structure comprises a thick-walled cylinder 38 that has an outside diameter which is slightly less than the inside diameter of a given tube 11 into which it is to be placed for plugging same. The interior of the plug 38 contains an explosive charge (not shown) with the arrangement such that there is a power charge near the nose end of the plug, while there are a plurality of sequential charges leading from a detonator charge to the power charge.

The specific arrangement of the charge and the related detonator and other charges is set up and designed for carrying out the desired expansion of the plug, without rupture of the walls thereof. This is important since a preferred embodiment of the invention relates to a use in hydrocarbon and other petroleum processes where there may be explosive fluids in one or both of the fluid paths through a heat exchanger wherein the invention is em- 'ployed. However, as already noted, all the design features including the size of charges employed, etc, form no part per se of the subject invention.

The walls of the plug, i.e. of cylinder 38 are formed of a ductile material, e.g. brass, that can withstand the forces of the explosive charge when detonated and readily deform so as to provide desired plugging action. Of course, it must be able to deform without setting up any undue stresses which would cause the walls of the plug to break, or otherwise provide ineffective sealing action particularly under substantial pressures.

An important feature of the invention is the employment of axial centering means for the plug. It has been found necessary to have a plug so centered within a tube in order to ensure even expansion and tight sealing of the tube end. Such centering means could take various different forms that are not necessarily mere mechanical equivalents of one another. For example, one manner (not illustrated) of centering of the plug body, could be to wrap tape around the body of the plug near each end thereof.

A preferred arrangement for centering the plugs is to use centering devices such as those illustrated. These are constructed of resilient material, such as spring steel, and take the form a spider 39 attached at the nose end of the plug and another spider 40 attached near the other end of the plug. It will be observed that the spiders 39 and 40 each have six legs 41 (see FIG. 3) and 42 (see FIG. 4) respectively. These legs extend radially and act to contact the walls of the tube and thus hold the plug body 38 'accurately centered within the tube prior to detonation thereof.

It will be appreciated that the length of the legs 41 and 42 of the spiders 39 and 40 will be such that they extend somewhat farther than the distance of the interior radius for a tube 11. In this manner these legs will be forcefully bent and thus provide positive force by spring :action in centering and holding the plug axially aligned within the tube when placed therein. This is illustrated in FIGURES 5 and 6. It will be noted that FIGURE 5 shows a plug in place prior to detonation while FIGURE 6 shows the same plug after the charge has been detonated and the body of the plug has consequently been expanded to fit tightly Within the tube 11. This is accomplished at the end of a tube 11 where it is surrounded by the tube sheet, e.g. tube sheet 23. Consequently, there is adequate support for the walls of the tube 11 to withstand the pressure of the explosion. Therefore, the plug expansion will cause a leak-proof seal at the tube walls within the tube sheet which holds the end of the tube.

The spiders 39 and 40 may be attached to the plug 38 in any feasible or convenient manner but, as illustrated, the nose spider 39 is preferably attached by means of a machine screw 43 that fits closely through a central hole 45 of the spider 39 and thus holds the spider securely in a centralized manner at the nose end of the plug. The spider 40 is attached at the other end of the plug body 38, e.g. by being fitted over a threaded hub 48 that is located extending coaxially from the plug body. This spider 40 may be held in place against axial displacement relative to the plug by means of a beveled nut 46.

In order to provide for electrical detonation of the charge in a plug, there is an electrical connector 49 that is integrally constructed with the body of the plug and should be tightly sealed in place to withstand the explosion pressure without rupture.

The electrical circuit for an electrical detonator element (not shown) is completed by employing the body of cylinder 38 and the hub 48 as one electrically conducting current path, while the other path includes the connector 49.

In order to insert a plug from the far end of a given tube 11, any tool that would include some means for det-onating the plug after it was positioned within the tube sheet, might be employed. However, a preferred tool having a high degree of flexibility is one like that illustrated in FIGURE 2. There is an electrically conductive material head 50 that is securely attached to one end of a hollow flexible shaft 51 which is preferably made of a tightly laid helix, as shown.

Within the head 50 there is a socket 56 which has a flared and smooth sided portion nearest the open end thereof. Then there is a short threaded section of the socket which is adapted to engage the threads of the hub 48 and hold the plug 38 in place on the end of the head 50 of the insertion tool.

As indicated above in connection with the structure of the plug itself, there is an electrically actuated detonator (not shown) and the circuit for applying current to fire it employs the case as one path and the connector 49 as the other path. Consequently, the one path is continued over the inserting tool via the threaded portion of the socket 56 and the body of the head 50 to an insulated wire 57 that has a bared end soldered to the head 50' as indicated in FIGURE 2.

The other path for supplying electrical current to fire the plug detonator is carried from the connector 49 to an electrically conductive sleeve 60 that is supported for frictional contact with the connector by means of an insulating material insert 61. This maintains electrical separation from the first described path that includes the head 50. The other electrical path is carried along the tool by another insulated wire 62 that has a bared end soldered to the sleeve 60, as indicated.

It will be noted that the cylindrical body 38 of the plug is constructed considerably longer than the thickness of the tube sheet 23, but the explosive charge arrangement within the plug is such that the expansion (by reason of the power charge) is concentrated near the nose end of the plug. Consequently, the expansion will take place largely within the thickness of the tube sheet which will easily withstand the expansive forces and thus help create the desired pressure proof plugging action.

In carrying out a method according to the invention, the following steps will be included. However, these are not necessarily all carried out in the order given, nor do they necessarily make up all of the steps which might be employed in carrying out a method according to the invention.

It will be appreciated that a method according to this invention is applicable to structures such as heat exchangers, where a tube is attached at at least one end thereof to a tube sheet. The steps of the method include:

(1) Taking an explosive type plug which has a charge therein;

(2) Inserting and coaxially centering such plug within the tube;

(3) Locating the plug longitudinally so that the power charge of the plug is within the tube sheet; and

(4) Detonating the charge so that the plug walls are caused to expand within the tube sheet and create a pressure tight seal at the tube where it is connected to the tube sheet.

It is to be noted that the second step may be carried out in various ways. These need not be mechanically equivalent to one another, e.g. the plug might be inserted by placing same within a tube and then applying a fluid pressure behind the plug to cause it to move through the tube for a desired distance therein, or a string might be run through the tube in such a way that the plug could be pulled into the tube to the desired location. However, a preferred manner of carrying out this step is that of pushing the plug through the tube, with a tool for providing such longitudinal pushing force, until the plug is located in the desired place prior to detonation.

Similarly, it is to be noted that the coaxial centering portion of this step, may be carried out by employing various structures that are not necessarily mechanically equivalent to one another. For example, it is envisaged that the plug might be placed in the tube and thereafter centered by inserting wedges as necessary. Another manner of centering the plug might be to wrap a soft tape around the ends of the plug so that it will be held centered as it is placed within the tube.

In this case, a preferred manner of carrying out this part of the step (centering the plug) is that of employing a pair of flexible spider means attached at the ends of the plug so that .these will physically hold the plug centered as it is pushed through the tube.

While particular embodiments of the invention have been described in considerable detail in accordance with the applicable statutes, this is not to be taken as in any way limiting the invention but merely as being descriptive thereof.

I claim:

1. An expansible plug for use in heat exchanger tubes or the like, comprising:

a thick-walled cylindrical body having closed ends and an outside diameter over the entire length thereof that is slightly less than the inside diameter of said tubes,

an explosive charge within said body,

said body being constructed of ductile material having sufiicient wall thickness to avoid rupture when said charge is detonated, and

means for detonating said charge when the plug is in place within a tube,

means for radially centering said plug Within said tube for coaxial relationship prior to detonation,

said radial centering means comprises a resilient centering device at each end of said plug body,

said resilient centering devices have at least three radial protrusions extending more than the length of the inside radius of said tube from the axis thereof,

said centering devices comprise flat spider means constructed of spring steel, and further including means for coaxially attaching said spider means to said cylindrical body adjacent to the ends thereof.

2. An expansible plug according to claim 1 wherein said spider means comprise thin stampings having six radial legs each, said legs being equally spaced apart circumferentially for accurate centering of the ends of said body.

References Cited UNITED STATES PATENTS 2,779,279 1/ 1957 Maiwurm. 3,175,618 3/1965 Lang et a1. 3,203,479 8/1965 Hindman 138-89 X 3,364,562 1/ 1968 Armstrong.

FOREIGN PATENTS 18,190 1904 Great Britain. 1,054,810 1/ 1967 Great Britain.

HERBERT F. ROSS, Primary Examiner US. Cl. X.R. 29421; 138-93 

